C-type natriuretic peptide is synthesized and secreted from leukemia cell lines, peripheral blood cells, and peritoneal macrophages

Sacubitril/Valsartan inhibits M1 type macrophages polarization in acute myocarditis by targeting C-type natriuretic peptide

Studies have shown that Sacubitril/valsartan (Sac/Val) can reduce myocardial inflammation in myocarditis mice, in addition to its the recommended treatment of heart failure. However, the underlying mechanisms of Sac/Val in myocarditis remain unclear. C-type natriuretic peptide (CNP), one of the targeting natriuretic peptides of Sac/Val, was recently reported to exert cardio-protective and anti-inflammatory effects in cardiovascular systems. Here, we focused on circulating levels of CNP in patients with acute myocarditis (AMC) and whether Sac/Val modulates inflammation by targeting CNP in experimental autoimmune myocarditis (EAM) mice as well as LPS-induced RAW 264.7 cells and bone marrow derived macrophages (BMDMs) models. Circulating CNP levels were higher in AMC patients compared to healthy controls, and these levels positively correlated with the elevated inflammatory cytokines IL-6 and monocyte count. In EAM mice, Sac/Val alleviated myocardial inflammation while augmenting circulating CNP levels rather than BNP and ANP, accompanied by reduction in intracardial M1 macrophage infiltration and expression of inflammatory cytokines IL-1β, TNF-α, and IL-6. Furthermore, Sac/Val inhibited CNP degradation and directly blunted M1 macrophage polarization in LPS-induced RAW 264.7 cells and BMDMs. Mechanistically, the effects might be mediated by the NPR-C/cAMP/JNK/c-Jun signaling pathway apart from NPR-B/cGMP/NF-κB pathway. In conclusion, Sac/Val exerts a protective effect in myocarditis by increasing CNP concentration and inhibiting M1 macrophages polarization.

C-type natriuretic peptide plasma levels and whole blood mRNA expression show different trends in adolescents with different degree of endothelial dysfunction

C-type natriuretic peptide (CNP) is an endogenous adipogenesis regulator whose plasma levels in childhood are known, while no data are available on its expression. Our aim was to evaluate both CNP plasma levels and CNP system expression in whole blood obtained from normal-weight (N, n = 24) and obese (O, n = 16) adolescents (age:13.5 ± 0.4 years). Endothelial function was assessed measuring reactive hyperemia index (RHI). CNP plasma levels, evaluated with specific RIA, resulted significantly lower in O than in N (6.1 ± 0.8 vs.15.2 ± 1.3 pg/mL; p < 0.0001), while CNP/NPR-B/NPR-C mRNA, measured by Real-Time PCR, resulted similar in N (4.1 ± 1.7; 5.0 ± 1.6; 2.2 ± 0.9) and in O (4.3 ± 1.6; 3.5 ± 1.1; 2.3 ± 0.8). RHI was significantly lower in O than in N (1.4 ± 0.08 vs.2.1 ± 0.04, p < 0.0001). Dividing all subjects according to the RHI median value, irrespective of the presence or absence of obesity (Group 1 > 1.9, n = 23, Group 2 < 1.9, n = 17), CNP plasma concentrations resulted significantly (p = 0.014) higher in Group 1 (14.6 ± 1.6) than in Group 2 (7.5 ± 1.0), showing a significant correlation with RHI (p = 0.0026), while CNP mRNA expression was, surprisingly, higher in Group 2 (7.0 ± 2.3) than in Group 1 (1.8 ± 0.4; p = 0.02). NPR-B mRNA resulted similar in both Groups (4.3 ± 1.6; 4.7 ± 1.3) and NPR-C significantly higher in Group 2 (p = 0.02). Our data suggest different trends between CNP plasma levels and expression, assessed for the first time in whole blood, that could reflect changes occurring both at CNP transcriptional level in activated leukocytes due to inflammation, and at circulating levels, due to CNP paracrine/autocrine activities. This could represent an interesting area for new therapies able to modulate endothelial dysfunction.

Dexamethasone increases production of C-type natriuretic peptide in the sheep brain

Although C-type natriuretic peptide (CNP) has high abundance in brain tissues and cerebrospinal fluid (CSF), the source and possible factors regulating its secretion within the central nervous system (CNS) are unknown. Here we report the dynamic effects of a single IV bolus of dexamethasone or saline solution on plasma, CSF, CNS and pituitary tissue content of CNP products in adult sheep, along with changes in CNP gene expression in selected tissues. Both CNP and NTproCNP (the amino-terminal product of proCNP) in plasma and CSF showed dose-responsive increases lasting 12-16 h after dexamethasone, whereas other natriuretic peptides were unaffected. CNS tissue concentrations of CNP and NTproCNP were increased by dexamethasone in all of the 12 regions examined. Abundance was highest in limbic tissues, pons and medulla oblongata. Relative to controls, CNP gene expression (NPPC) was upregulated by dexamethasone in 5 of 7 brain tissues examined. Patterns of responses differed in pituitary tissue. Whereas the abundance of CNP in both lobes of the pituitary gland greatly exceeded that of brain tissues, neither CNP nor NTproCNP concentration was affected by dexamethasone, despite an increase in NPPC expression. This is the first report of enhanced production and secretion of CNP in brain tissues in response to a corticosteroid. Activation of CNP secretion within CNS tissues by dexamethasone, not exhibited by other natriuretic peptides, suggests an important role for CNP in settings of acute stress. Differential findings in pituitary tissues likely relate to altered processing of proCNP storage and secretion.

Biomarkers for differentiation of causes of respiratory distress in dogs and cats: Part 2--Lower airway, thromboembolic, and inflammatory diseases

OBJECTIVES

To review the current veterinary and relevant human literature regarding biomarkers of respiratory diseases leading to dyspnea and to summarize the availability, feasibility, and practicality of using respiratory biomarkers in the veterinary setting.

DATA SOURCES

Veterinary and human medical literature: original research articles, scientific reviews, consensus statements, and recent textbooks.

HUMAN DATA SYNTHESIS

Numerous biomarkers have been evaluated in people for discriminating respiratory disease processes with varying degrees of success.

VETERINARY DATA SYNTHESIS

Although biomarkers should not dictate clinical decisions in lieu of gold standard diagnostics, their use may be useful in directing care in the stabilization process. Serum immunoglobulins have shown promise as an indicator of asthma in cats. A group of biomarkers has also been evaluated in exhaled breath. Of these, hydrogen peroxide has shown the most potential as a marker of inflammation in asthma and potentially aspiration pneumonia, but methods for measurement are not standardized. D-dimers may be useful in screening for thromboembolic disease in dogs. There are a variety of markers of inflammation and oxidative stress, which are being evaluated for their ability to assess the severity and type of underlying disease process. Of these, amino terminal pro-C-type natriuretic peptide may be the most useful in determining if antibiotic therapy is warranted. Although critically evaluated for their use in respiratory disorders, many of the biomarkers which have been evaluated have been found to be affected by more than one type of respiratory or systemic disease.

CONCLUSION

At this time, there are point-of-care biomarkers that have been shown to reliably differentiate between causes of dyspnea in dogs and cats. Future clinical research is warranted to understand of how various diseases affect the biomarkers and more bedside tests for their utilization.

Serial Evaluation of Abdominal Fluid and Serum Amino-terminal pro-C-type Natriuretic Peptide in Dogs with Septic Peritonitis

Background

Serum N‐terminal pro‐C‐natriuretic peptide (NT‐proCNP) has shown promise as a diagnostic biomarker for sepsis. Its sensitivity to detect dogs with septic peritonitis (SP) is reportedly low, perhaps attributable to the compartmentalization of NT‐proCNP in the abdominal cavity.

Objectives

To evaluate the use of an ELISA for the measurement of NT‐proCNP in canine abdominal fluid and to describe the peri‐operative pattern of abdominal fluid and serum NT‐proCNP concentrations in dogs with SP.

Animals

Five client‐owned dogs with nonseptic abdominal effusion of varying etiologies and 12 client‐owned dogs with SP undergoing abdominal surgery and placement of a closed‐suction abdominal drain (CSAD). Six dogs were included upon hospital admission; 6 were included the day after surgery.

Methods

Prospective pilot study. A commercially available ELISA kit was analytically validated for use on canine abdominal fluid. The NT‐proCNP concentrations were measured in the abdominal fluid of control dogs, and in serum and abdominal fluid of dogs with SP from admission for CSAD removal.

Results

In dogs with SP, admission abdominal fluid NT‐proCNP concentrations were lower than the concurrent serum concentrations (P = 0.031), and lower than control canine abdominal fluid concentrations (P = 0.015). Postoperatively, abdominal fluid NT‐proCNP concentrations remained lower than serum concentrations (P < 0.050), except on day 4.

Conclusions and Clinical Importance

The ELISA kit was able to measure NT‐proCNP in canine abdominal fluid. In dogs with SP, low serum NT‐proCNP concentrations cannot be explained by abdominal compartmentalization.

N-terminal pro-C-natriuretic peptide and cytokine kinetics in dogs with endotoxemia

BACKGROUND

Serum N-terminal pro-C-natriuretic peptide (NT-proCNP) concentration at hospital admission has sufficient sensitivity and specificity to differentiate naturally occurring sepsis from nonseptic systemic inflammatory response syndrome (SIRS). However, little is known about serum NT-proCNP concentrations in dogs during the course of sepsis.

OBJECTIVE

To determine serum NT-proCNP and cytokine kinetics in dogs with endotoxemia, a model of canine sepsis.

SAMPLES

Eighty canine serum samples.

METHODS

Eight healthy adult Beagles were randomized to receive Escherichia coli lipopolysaccharide (LPS, 5 μg/kg) or placebo (0.9% NaCl) as a single IV dose in a randomized crossover study. Serum collected at 0, 1, 2, 4, and 24 hours was stored at -80°C for batch analysis. Serum NT-proCNP was measured by ELISA and 13 cytokines and chemokines by multiplex magnetic bead-based assay.

RESULTS

Serum NT-proCNP concentrations did not differ significantly between LPS- and placebo-treated dogs at any time. When comparing serum cytokine concentrations, LPS-treated dogs had higher interleukin-6 (IL-6), IL-10, TNF-α and KC-like at 1, 2, and 4 hours; higher CCL2 at 1, 2, 4, and 24 hours; and higher IL-8 and CXCL10 at 4 hours compared to placebo-treated dogs. There were no differences in serum GM-CSF, IFN-γ, IL-2, IL-7, IL-15 or IL-18 between LPS- and placebo-treated dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

Serum NT-proCNP concentration does not change significantly in response to LPS administration in healthy dogs. Certain serum cytokine and chemokine concentrations are significantly increased within 1-4 hours after LPS administration and warrant further investigation as tools for the detection and management of sepsis in dogs.

Biomarkers predicting sepsis in polytrauma patients: Current evidence

INTRODUCTION

Major trauma still represents one of the leading causes of death in the first four decades of life. Septic complications represent the predominant causes of late death (45% of overall mortality) in polytrauma patients. The ability of clinicians to early differentiate between systemic inflammatory response syndrome (SIRS) and sepsis is demonstrated to improve clinical outcome and mortality. The identification of an "ideal" biomarker able to early recognize incoming septic complications in trauma patients is still a challenge for researchers.

AIM

To evaluate the existing evidence regarding the role of biomarkers to predict or facilitate early diagnosis of sepsis in trauma patients, trying to compile some recommendations for the clinical setting.

METHODS

An Internet-based search of the MEDLINE, EMBASE and Cochrane Library databases was performed using the search terms: "Biomarkers", "Sepsis" and "Trauma" in various combinations. The methodological quality of the included studies was assessed using the Quality Assessment of Diagnostic Accuracy Studies Checklist (QUADAS). After data extraction, the level of evidence available for each bio-marker was rated and presented using the "best-evidence synthesis" method, in line with the US Agency for Healthcare Research and Quality.

RESULTS

Thirty studies were eligible for the final analysis: 13 case-control studies and 17 cohort studies. The "strong evidence" available demonstrated the potential use of procalcitonin as an early indicator of post-traumatic septic complications and reported the inability of c-reactive protein (CRP) to specifically identify infective complications. Moderate, conflicting and limited evidence are available for the other 31 biomarkers.

CONCLUSION

Several biomarkers have been evaluated for predicting or making early diagnosis of sepsis in trauma patients. Current evidence does not support the use of a single biomarker in diagnosing sepsis. However, procalcitonin trend was found to be useful in early identification of post-traumatic septic course and its use is suggested (Recommendation Grade: B) in clinical practice.

C-type natriuretic peptide: a new cardiac mediator

Natriuretic peptides are endogenous hormones released by the heart in response to myocardial stretch and overload. While atrial and brain natriuretic peptides (ANP, BNP) were immediately considered cardiac hormones and their role was well-characterized and defined in predicting risk in cardiovascular disease, evidence indicating the role of C-type natriuretic peptide (CNP) in cardiovascular regulation was slow to emerge until about 8 years ago. Since then, considerable literature on CNP and the cardiovascular system has been published; the aim of this review is to examine current literature relating to CNP and cardiovascular disease, in particular its role in heart failure (HF) and myocardial infarction (MI). This review retraces the fundamental steps in research that led understanding the role of CNP in HF and MI; from increased CNP mRNA expression and plasmatic concentrations in humans and in animal models, to detection of CNP expression in cardiomyocytes, to its evaluation in human leukocytes. The traditional view of CNP as an endothelial peptide has been surpassed by the results of many studies published in recent years, and while its physiological role is still under investigation, information is now available regarding its contribution to cardiovascular function. Taken together, these observations suggest that CNP and its specific receptor, NPR-B, can play a very important role in regulating cardiac hypertrophy and remodeling, indicating NPR-B as a new potential drug target for the treatment of cardiovascular disease.

Gene expression of C-type natriuretic peptide and of its specific receptor NPR-B in human leukocytes of healthy and heart failure subjects

C-type natriuretic peptide (CNP), a member of the family of natriuretic peptides, is synthesized and secreted from monocytes and macrophages that resulted to be a source of CNP at inflammatory sites. This suggests that special attention should be focused on the possible role of CNP in the immune system, in addition to its effects on the cardiovascular system. The aim of this study was to evaluate the possibility of measuring the mRNA expression of CNP and NPR-B, its specific receptor, in human whole blood samples of healthy (N; n=7) and heart failure (HF; n=7) subjects by Real-Time PCR (RT-PCR). Total RNA was extracted from leukocytes with QIAamp RNA Blood Kit and/or with PAXgene Blood RNA Kit. RT-PCR was performed and optimized for each primer. The experimental results were normalized with the three most stably expressed genes. CNP and NPR-B expression trend was similar in both fresh and frozen human whole blood. Significant higher levels of CNP and NPR-B mRNA expression were found in HF patients with respect to controls (CNP: N=1.23±0.33 vs. HF=6.54±2.09 p=0.027; NPR-B: N=0.85±0.23 vs. HF=5.31±1.98 p=0.04). A significant correlation between CNP and NPR-B (r=0.86, p<0.0001) was observed. Further studies are needed to clarify the pathophysiological properties of this peptide but the possibility to measure CNP and NPR-B mRNA expression in human leukocytes with a fast and easy procedure is a useful starting point for future investigation devoted to better understand the biomolecular processes associated to different diseases.

Regulation of C-type natriuretic peptide expression

C-type natriuretic peptide (CNP) is a member of the small family of natriuretic peptides that also includes atrial natriuretic peptide (ANP) and brain, or B-type natriuretic peptide (BNP). Unlike them, it performs its major functions in an autocrine or paracrine manner. Those functions, mediated through binding to the membrane guanylyl cyclase natriuretic peptide receptor B (NPR-B), or by signaling through the non-enzyme natriuretic peptide receptor C (NPR-C), include the regulation of endochondral ossification, reproduction, nervous system development, and the maintenance of cardiovascular health. To date, the regulation of CNP gene expression has not received the attention that has been paid to regulation of the ANP and BNP genes. CNP expression in vitro is regulated by TGF-β and receptor tyrosine kinase growth factors in a cell/tissue-specific and sometimes species-specific manner. Expression of CNP in vivo is altered in diseased organs and tissues, including atherosclerotic vessels, and the myocardium of failing hearts. Analysis of the human CNP gene has led to the identification of a number of regulatory sites in the proximal promoter, including a GC-rich region approximately 50 base pairs downstream of the Tata box, and shown to be a binding site for several putative regulatory proteins, including transforming growth factor clone 22 domain 1 (TSC22D1) and a serine threonine kinase (STK16). The purpose of this review is to summarize the current literature on the regulation of CNP expression, emphasizing in particular the putative regulatory elements in the CNP gene and the potential DNA-binding proteins that associate with them.

Evaluation of serum NT-pCNP as a diagnostic and prognostic biomarker for sepsis in dogs

BACKGROUND

There is a need for diagnostic biomarkers that can rapidly differentiate dogs with sepsis from dogs with noninfectious forms of systemic inflammatory response syndrome (NSIRS).

OBJECTIVES

To compare serum NT-pCNP concentrations among dogs with various forms of sepsis, NSIRS, and healthy controls and to evaluate the use of serum NT-pCNP for the diagnosis of various forms of sepsis in dogs.

ANIMALS

One hundred and twelve dogs including 63 critically ill dogs (sepsis n = 29; NSIRS n = 34) and 49 healthy control dogs.

METHODS

Prospective clinical investigation. Serum samples were collected for NT-pCNP measurement from dogs with sepsis or NSIRS within 24 hours of intensive care unit admission or at the time of presentation for healthy dogs. Dogs with sepsis were subclassified based on the anatomic region of infection. Serum NT-pCNP concentrations were compared among sepsis, NSIRS and healthy groups as well as among sepsis subgroups. The area under the curve (AUC), sensitivity, and specificity for identifying dogs with sepsis were determined.

RESULTS

Using a cut-off value of 10.1 pmol/L, AUC, sensitivity, and specificity of NT-pCNP for differentiating dogs with sepsis from dogs with NSIRS or healthy control dogs were 0.71 (95% CI, 0.58-0.85), 65.5% (45.7-82.1%), and 89.2% (80.4-94.9%), respectively. Serum NT-pCNP had poor sensitivity for peritoneal sources of sepsis; AUC [0.92 (0.81-1.0)], sensitivity [94% (71-100%)], and specificity [89% (80-95%)] improved when these dogs were excluded. Serum NT-pCNP concentration was not associated with survival in the sepsis group.

CONCLUSIONS AND CLINICAL IMPORTANCE

Serum NT-pCNP is a promising diagnostic biomarker for sepsis but is a poor indicator of septic peritonitis.

C-type natriuretic-derived peptides as biomarkers in human disease

The natriuretic peptide system comprises three structurally related peptides: atrial natriuretic peptide, B-type natriuretic peptide and C-type natriuretic peptide. In circulation, they play an important endocrine role in the regulation of cardiovascular homeostasis by maintaining blood pressure and extracellular fluid volume. Atrial natriuretic peptide and B-type natriuretic peptide have gained considerable diagnostic interest as biomarkers in cardiovascular disease. By contrast, C-type natriuretic peptide has not yet been ascribed a role in human diagnostics. This perspective aims at recapitulating the present biochemical and clinical issues concerning C-type natriuretic peptide measurement in plasma as a potential biomarker.

Translational research of C-type natriuretic peptide (CNP) into skeletal dysplasias

By using transgenic and knockout mice, we have elucidated that C-type natriuretic peptide (CNP) is a potent stimulator of endochondral bone growth. In humans, loss-of-function mutations in the gene coding for guanylyl cyclase-B (GC-B), the specific receptor for CNP, have been proved to be the cause of acromesomelic dysplasia, type Maroteaux, one form of human skeletal dysplasias. Following these results, we have started to translate the stimulatory effect of CNP on endochondral bone growth into the therapy for patients with skeletal dysplasias. We have shown that targeted overexpression of CNP in cartilage or systemic administration of CNP reverses the impaired skeletal growth of mice model of achondroplasia, the most common form of human skeletal dysplasias.

ProCNP and CNP are expressed primarily in male genital organs

Lack of knowledge about the cellular origin of C-type natriuretic peptides (CNP) in the body has hampered the understanding of their biology. We examined the tissue specific expression of proCNP and CNP in the pig. The concentration of the CNP precursor, proCNP, was measured in extracts of 32 different tissues using a newly developed RIA. In 22 tissue extracts, we also measured CNP using a commercial RIA. In selected tissues, CNP mRNA was quantified by PCR, and the cellular CNP and proCNP localization was visualized by immunocytochemistry. Extracts from selected tissues were examined by gel chromatography. The highest peptide concentrations were found in extracts from the epididymis, seminal vesicles and prostate. CNP mRNA in the seminal vesicles and epididymis was 125-fold higher than in the other tissues examined. Gel chromatography showed that a CNP-53-like peptide is the dominant CNP tissue-form. Immunocytochemistry confirmed the pattern of peptide expression measured by RIA. In conclusion most proCNP-derived peptides are synthesized in epithelial cells in the epididymis, the prostate gland and in the seminal vesicles. The expression in male genital organs suggests a role of CNP in reproduction.

Sphingosine-1-phosphate receptor expression in cardiac fibroblasts is modulated by in vitro culture conditions

The bioactive molecule sphingosine-1-phosphate (S1P) binds with high affinity to five recognized receptors (S1P(1-5)) to affect various tissues, including cellular responses of cardiac fibroblasts (CFbs) and myocytes. CFbs are essential components of myocardium, and detailed study of their cell signaling and physiology is required for a number of emerging disciplines. Meaningful studies on CFbs, however, necessitate methods for selective, reproducible cell isolations. Macrophages reside within normal cardiac tissues and often are isolated with CFbs. A protocol was therefore developed that significantly reduces macrophage levels and utilizes more CFb-specific markers (discoidin domain receptor-2) instead of, or in addition to, more commonly used cytoskeletal markers. Our results demonstrate that primary isolated, purified CFbs express predominantly S1P(1-3); however, the relative levels of these receptor subtypes are modulated with time and by culture conditions. In coculture experiments, macrophages altered CFb S1P receptor levels relative to controls. Further investigations using known macrophage-secreted factors showed that S1P and H(2)O(2) had minimal effects on CFb S1P(1-3) expression, whereas transforming growth factor-beta1, TNF-alpha, and PDGF-BB significantly altered all S1P receptor subtypes. Lowering FBS concentrations from 10% to 0.1% increased S1P(2), whereas supplementation with either PDGF-BB or Rho-associated protein kinase inhibitor Y-27632 significantly elevated S1P(3) levels. S1P(2) and S1P(3) receptor levels are known to regulate cell migration. Using cells isolated from either normal or S1P(3)-null mice, we demonstrate that S1P(3) is important and necessary for CFb migration. These results highlight the importance of demonstrating CFb culture purity in functional studies of S1P and also identify conditions that modulate S1P receptor expression in CFbs.

Identification, regulation and anti-proliferative role of the NPR-C receptor in gastric epithelial cells

Evidence suggests that functional atrial natriuretic peptide (ANP) receptors occur in surface gastric mucosal epithelial cells. To evaluate functional aspects of ANP in a model of these cells we examined the expression of natriuretic peptide receptors (NPR) subtypes A and C in the non-transformed rat gastric mucosal epithelial cell line RGM1. Transcripts for NPR-A and NPR-C were detected in RGM1 cells by RT-PCR. However, only NPR-C protein was detected by Western blot and immunohistochemical analyses. Specific saturable binding of (125)I-ANP to RGM1 cells revealed a single class of high affinity binding sites (K (d) = 208 +/- 71pM, B (max) = 110,000 +/- 14,000 sites/cell, Hill coefficient = 0.97 +/- 0.05). ANP (IC(50) 130 +/- 47pM), BNP (IC(50) 716 +/- 26 pM), CNP (IC(50) 356 +/- 85pM) and C-ANP (IC(50) 134 +/- 13pM), a specific ligand for NPR-C, effectively displaced (125)I-ANP binding. Cross-linking of (125)I-ANP to cells labeled predominantly a protein of 66,000 Da. These data suggest that (125)I-ANP binding was primarily to NPR-C. ANP and C-ANP inhibited forskolin- and prostaglandin E(2) (PGE(2))-stimulated cAMP in a PTx-sensitive fashion. PGE(2), transforming growth factor-+/-1 (TGF-+/-1), forskolin, 8-bromo-cyclic AMP, and phorbol-12-myristate-13-acetate (PMA) caused a dose-dependent decrease in specific (125)I-ANP binding, whereas epidermal growth factor (EGF), 8-bromo-cyclic GMP and 4+/--phorbol didecanoate had no effect. PGE(2), forskolin, TGF-+/-1 and PMA significantly decreased (125)I-ANP B (max) values, NPR-C protein and steady-state NPR-C transcript levels. H89, a protein kinase A inhibitor, blocked the reduction of NPR-C mRNA produced by both forskolin and PGE(2.) GF109203X, a protein kinase C inhibitor, abolished the PMA-induced decrease in NPR-C transcripts but only partially blocked that produced by TGF-+/-1. RGM1 cells exhibited a dose-dependent decrease in both DNA synthesis and cell proliferation when cultured in the presence of ANP or C-ANP. These findings indicate that RGM1 cells express functional NPR-C receptors that can influence RGM1 cell proliferation and are down-regulated by PGE(2) and TGF-+/-1.